Levonorgestrel is a manufactured hormone used in a number of birth control methods. In pill form, sold under the brand name Plan B among others, it is useful within 120 hours as emergency birth control. It becomes less effective the longer after sex and only works before pregnancy has occurred. It is also combined with an estrogen to make combined oral birth control pill. Within an IUD, sold as Mirena among others, it is effective for long term prevention of pregnancy. An implantable form of levonorgestrel is also available in some countries.
Common side effects include nausea, breast tenderness, headaches, and increased, decreased, or irregular menstrual bleeding. When used as a form of emergency contraception, if pregnancy occurs, there is no evidence its use harms the baby. It is safe to use during breastfeeding. Birth control that contains levonorgestrel will not change the risk of sexually transmitted infections. It works mostly by decreasing ovulation and closing off the cervix to prevent the passage of sperm.
Levonorgestrel was first made in the 1960s and its use as a method of birth control began in the 1980s. It is on the World Health Organization's List of Essential Medicines, the most effective and safe medicines needed in a health system. It is available as a generic medication. The wholesale cost in the developing world costs between 0.23 and 1.65 USD for the dose required for emergency birth control. In the United States it is over the counter for all ages.
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Medical uses
Birth control pills
At low doses, levonorgestrel is used in monophasic and triphasic formulations of combined oral contraceptive pills, with available monophasic doses ranging from 100-250 µg, and triphasic doses of 50 µg/75 µg/125 µg.
At very low daily dose of 30 µg, levonorgestrel is used in some progestogen only pill formulations.
Emergency birth control
Levonorgestrel is used in emergency contraceptive pills (ECPs), both in a combined Yuzpe regimen which includes estrogen, and as a levonorgestrel-only method. The levonorgestrel-only method uses levonorgestrel 1.5 mg (as a single dose or as two 0.75 mg doses 12 hours apart) taken within 3 days of unprotected sex, with one study indicating that beginning as late as 120 hours (5 days) after intercourse could be effective.
The primary mechanism of action of levonorgestrel as a progestogen-only emergency contraceptive pill is, according to International Federation of Gynecology and Obstetrics (FIGO), to prevent fertilization by inhibition of ovulation and thickening of cervical mucus. FIGO has stated that: "review of the evidence suggests that LNG [levonorgestreol] ECPs cannot prevent implantation of a fertilized egg. Language on implantation should not be included in LNG ECP product labeling." In November 2013, the European Medicines Agency (EMA) approved a change to the label saying it cannot prevent implantation of a fertilized egg.
Other studies still find the evidence to be unclear. While it is unlikely that emergency contraception affects implantation it is impossible to completely exclude the possibility of post-fertilization effect.
In November 2013, the EMA also approved a change to the label for HRA Pharma's NorLevo saying: "In clinical trials, contraceptive efficacy was reduced in women weighing 75 kg [165 pounds] or more, and levonorgestrel was not effective in women who weighed more than 80 kg [176 pounds]." In November 2013 and January 2014, the FDA and the EMA said they were reviewing whether increased weight and body mass index (BMI) reduce the efficacy of emergency contraceptives.
Intrauterine device
Levonorgestrel is the active ingredient in a number of intrauterine devices including Mirena and Skyla.
Birth control implant
Levonorgestrel is the active ingredient in Norplant and Jadelle.
Hormone replacement therapy
Levonorgestrel is combined with 17-beta estradiol in the estrogen patch.
Side effects
After intake of levonorgestrel 1.5 mg in clinical trials, very common effects (reported by 10% or more) included: dizziness, headache, nausea, abdominal pain, uterine pain, delay of menstruation, heavy menstruation, uterine bleeding, or fatigue; common effects (reported by 1% to 10%) included diarrhea, vomiting, or painful menstruation; these effects usually disappeared within 48 hours.
Chemistry
Levonorgestrel is an estrane steroid derived from testosterone and is also known as 17?-ethynyl-18-methyl-19-nortestosterone or as 17?-ethynyl-18-methylestr-4-en-17?-ol-3-one. Levonorgestrel (levo=left) is one form of a steroid, norgestrel, that exists in two mirror image left and right forms (see Chirality (chemistry)). It is the hormonally active levorotatory enantiomer of the racemic mixture. It is a gonane progestin derived from 19-nortestosterone.
Its in vitro relative binding affinities at human steroid hormone receptors are: 323% that of progesterone at the progesterone receptor, 58% that of testosterone at the androgen receptor, 17% that of aldosterone at the mineralocorticoid receptor, 7.5% that of cortisol at the glucocorticoid receptor, and <0.02% that of estradiol at the estrogen receptor.
If taken together with drugs that induce the CYP3A4 cytochrome liver enzyme, levonorgestrel may be metabolized faster and may have lower efficacy.
History
Levonorgestrel was first introduced in 1968, as an oral contraceptive in combination with ethinylestradiol.
Society and culture
Names
Levonorgestrel is also chemically known as l-norgestrel and D-norgestrel. It is often referred to as the "morning after pill".
There are many brand names for levonorgestrel-only ECPs, including: Nogestat, AfterPill, Escapelle, Plan B, Levonelle, Glanique, NorLevo, Postinor-2, i-pill, Next Choice, 72-HOURS.
Over-the-counter
In 2013 the FDA approved Plan B One-Step to be sold without a prescription with no age restriction.
Indian Health Services
A policy update in 2015 required all Indian Health Services-run pharmacies, clinics, and emergency departments to have Plan B One-Step in stock, to distribute it to any woman (or her representative) who asked for it without a prescription, age verification, registration or any other requirement, to provide orientation training to all staff regarding the medication, to provide unbiased and medically accurate information about emergency contraception, and to make someone available at all times to distribute the pill in case the primary staffer objected to providing it on religious or moral grounds.
Source of the article : Wikipedia
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